Honestly , I have zero issue with him being a rogue, and the OPs arguments are specious to be kind.
I *had* no problem with him being a vampire... until I read this thread. Those arguments are very sound. The suggestion of simply making him a vampire thrall is elegant and fixes a ton of issues.
Honestly my bigger issue was him being a vampire AND an Elf. It’s a hat on a hat. There comes a point when you have so many rare background elements that it strains all credulity. Just make him a human. The party needs more humans. Toril is a human dominated world. Not everyone is a super rare snowflake. Plus being an elf doesn’t play into his character one bit. It’s purely cosmetic. You could make him a human and not change a single line off dialogue.
Well, elf would explain why he was a vampire thrall ( not vampire spawn ) for centuries.
I do not think an evil master would use magic to make his minions live longer, especially if we talk about a lv1 rogue.
Prof. Dr. Dr. Mad S. Tist 
